1. Field Of The Invention
The invention relates to a small-sized electric motor used for, for example, driving a window glass in a power window system of an automobile, and in particular to a fitting structure for a brush supplying an electric current to a commutator on an armature.
2. Description Of The Prior Art
Heretofore, such a brush of a small-size electric motor has been installed to the motor as shown in FIG. 6 and FIG. 7.
That is, a small-sized electric motor 100 shown in FIGS. 6 and 7 is provided with an armature 102 rotatably in the motor case 101 and with a gear case 104 united with the motor case 101 by bolts 103. An armature shaft 102a of the armature 102 passes through an armature shaft hole 104a provided in the gear case 104 and a worm 102b is provided on the armature shaft 102a protruding from the side of the motor case 101. The worm 102b of the armature shaft 102a meshes with a worm wheel 105 housed rotatably in a cavity 104b of the gear case 104 and fixed to an output shaft 106.
The motor 100 is provided with a holder base 107 fixed on the left end of the gear case 104 in FIG. 6 by an annular projection 101a formed on the inner periphery of the motor case 101. Brushes 108 and 108', for supplying an electric current to the armature 102 by contact with a commutator 102c of the armature 102, are fitted to one end of respective brush holders 109 and 109', and another end of respective brush holders 109 and 109' are fixed to respective terminals 111 and 111' through joints 110 and 110' welded by spot welding, for example.
The respective terminals 111 and 111' (In FIG. 7, one the terminal 111 is shown since the terminal 111' is similar to the terminal 111.) are fixed to the holder base 107 by pressing projections 111a (and 111a') provided on the terminals 111 (and 111') on the side of the holder base 107 into terminal holes 107a (and 107a') provided on the holder base 107 forcing pawls 111b (and 111b') formed on projections 111a (111a') to bite into side walls 107b (and 107b') of the terminal holes 107a (and 107a').
Upon supplying a prescribed electric current through external wiring 112 and 113 connected to the respective terminals 111 and 111' by changing a switch (not shown), the electric current flows from one side terminal 111 to the other side terminal 111' through the brush holder 109, the brush 108, the commutator 102c, the armature 102, the commutator 102c, the brush 108' and the brush holder 109', the armature 102 rotates. Thereby, the worm wheel 105 meshed with the worm 102b provided an the armature shaft 102a of the armature 102 rotates together with the output shaft 106, and a window glass linked with the output shaft 106 can be driven in the opening or closing direction according to the changing of the switch in the case of applying the motor 100 to a power window system, for example.
However, in the conventional fitting structure for the brushes 108 and 108' the small-sized electric motor 100, because the respective brush holders 109 and 109' fitted with the brushes 108 and 108' are fixed to the respective terminals 111 and 111' through the joints 110 and 110' formed by welding such as spot welding, there is a decreasing tendency in the positioning accuracy at the time of placing the brushes 108 and 108' into contact with the commutator 102c of the armature 102. Therefore, there is a problem, since it is difficult to correct the brushes 108 and 108' into the predetermined position when the deviation occurs in the setting position. Furthermore, because the respective terminals 111 and 111' are fixed to the holder base 107 by pressing projections 111a and 111a' into terminal holes 107a and 107a' provided to the holder base 107 and forcing pawls 111b and 111b' formed on the respective projections 111a and 111a' to bite into side walls 107b and 107b' of the terminal holes 107a and 107a' there is another problem, since there is the possibility that the holder base 107 is deformed by the high stress applied on the side walls 107b and 107b' of the terminal hole 107a and 107a' at the time of pressing the respective projections 111a and 111a' into the terminal holes 107a and 107a'. Accordingly, there have been strong requirements to improve the positioning accuracy at the time of fixing the brush holder to the terminal and to reduce the stress applied on the holder base at the time of fixing the terminal to the holder base.